Hydrogen-Induced Effects on Tensile Properties and Impact Toughness in Additively Manufactured vs. Wrought Austenitic Stainless Steels

The growing demand for hydrogen-based energy systems has intensified the need for structural materials with enhanced resistance to hydrogen-induced degradation. This study presents a comparative investigation of hydrogen-induced mechanical behavior and embrittlement susceptibility of laser powder bed fusion (LPBF) manufactured 316L steel and conventionally manufactured (CM) 316H steel. Tensile/Charpy testing, hydrogen charging (up to 115 h), OM, SEM, TEM, and EBSD analysis were employed to assess microstructure, strength, ductility, fracture characteristics, and phase stability. In the uncharged state, LPBF steel exhibited significantly higher strength but lower ductility than CM steel, attributed to its fine cellular sub-grain microstructure. Both steels showed similar hydrogen saturation kinetics, reaching ~9 ppm, with residual hydrogen levels of ~3.3 ppm after 90 days of desorption. Hydrogen exposure led to a more pronounced degradation of the tensile properties of the LPBF steel, with an up to 22% reduction in the ductility-based embrittlement index, while CM steel remained much less affected. Impact toughness in both materials resisted hydrogen embrittlement, retaining over 96% of initial values. Fractographic analysis of tensile specimens revealed subsurface brittle zones consistent with calculated hydrogen diffusion depths. EBSD data indicated that hydrogen-stabilized austenite in LPBF steel was achieved by suppressing deformation-induced martensitic transformation, despite increased dislocation activity. These findings suggest that, while LPBF steel is more vulnerable to hydrogen embrittlement under tensile loading via the HELP mechanism, its microstructure mitigates impact toughness degradation through hydrogen-induced austenite stabilization.